Field of the Invention
The present invention relates to a diffusing plate having a microlens array. More specifically, the present invention relates to a diffusing plate used for the focusing of a finder system of a single lens reflex camera or the like.
Description of the Related Art
Hitherto, there has been known a diffusing plate on which many microlenses are arranged. However, in a diffusing plate that is used for the focusing of a finder system of a single lens reflex (SLR) camera or the like and on which many microlenses are arranged, the direction of diffracted light is limited to a particular direction, and the blur quality may become unnatural. When used together with a Fresnel lens, such a diffusing plate causes interference with the zonal structure of the Fresnel lens, and moire fringes may be generated. For this reason, a diffusing plate in which the distance between microlenses is changed has been proposed as disclosed in Japanese Patent Laid-Open No. 63-221329, and a diffusing plate in which the height of the vertices of microlenses is changed has been proposed as disclosed in Japanese Patent Laid-Open No. 03-192232.
However, in order to make unnaturalness of blur quality and moire fringes less noticeable, it is necessary to break the periodicity due to the change in the distance between microlenses described in Japanese Patent Laid-Open No. 63-221329 or the change in the height of the vertices of microlenses described in Japanese Patent Laid-Open No. 03-192232. However, the breaking of periodicity has the following problems. When a variation is created in the distance between microlenses, the whole diffusing plate divides into a part in which microlenses are densely arranged (dense part), and a part in which microlenses are sparsely arranged (sparse part). Light passes through the sparse part without being diffused. Therefore, if the sparse part increases, focusing becomes difficult. When a variation is created in the height of the vertices of microlenses, the diffusion angle of outgoing light is large between a microlens whose vertex is high and a microlens whose vertex is low, a light beam reaches the outside of the pupil of the finder, and therefore the finder image tends to become dark.
The present invention provides a diffusing plate having a microlens array in which unnaturalness of blur quality and moire fringes are less noticeable, with which focusing can be easily carried out. In this manner, a finder that is bright is achieved.